In a number of conventional vacuum cleaners the air in the cleaner casing is discharged by a moter fan, so that the pressure in the casing is lower than atmospheric pressure. A high speed air stream is formed by this air pressure differential, causing the corrupt air including dust to be inhaled through a dust in-let plate and flexible hose with an air suction hole, and passed to a filter unit with a solid filter of paper or cloth. This solid filter system has many problems, and has to be cleaned or have the filter changed after use.
As the fine pores of the air filter are clogged by dust, the intake air power of the machine declines rapidly. Most of the large particles of dust are intercepted by the filter but micro particles are passed through the filter with the air and returned to diffuse back into the room.
Thus, the room air becomes more turbid and harmful to the health.
Also the conventional solid filter system, is by nature such that there is a tradeoff between air in-let force and filter rate.
That is, filter rate is lower when the filter is coarse for achieving a higher air inlet force. The air in-let force is lower when the filter is dense for achieving a higher filter rate.